Soil Biota

Soils are populated by a multitude of microbial and invertebrate organisms, in addition to more complex
animal biota. Plant roots, seeds, and fungi, are a large part of this microhabitat.

Soil microorganisms play an extensive role in the decomposition of organic matter and production of
humus, cycling of nutrients and energy and elemental fixation, soil metabolism, and the production of
compounds that cause soil aggregates to form. Many are in symbiotic relationships with plants and
animals serving as nitrogen fixers and gut microbes. They function as a substantial part of the food
web.

Among the microorganisms found in the soil are bacteria, actinomycetes, fungi, micro-algae, protozoa,
nematodes, and other invertebrates (mostly arthropods).

It has been estimated that if you look at one “gram” of soil you will see the following numbers of
organisms--bacteria 10 8-9 , actinomycetes 105-8 , fungi 105-6 , micro-algae 103-6 , protozoa 103-5 ,
nematodes 101-2 , other invertebrates 103-5 . A square meter of soil may contain 30-300 earthworms.
There are more organisms in a gram of soil than there are human beings on this Earth!